Recently, various types of financial services, such as electronic money, have become more widespread as mobile information terminals have gained higher functionality. In addition, as mobile information terminals have gained higher functionality, the terminals have been used to store many pieces of private information, such as addresses, emails, photos, and website browsing history. Conventionally, security has been maintained for information handled with mobile information terminals by authentication (hereafter called log-in authentication) performed when starting to use the mobile information terminals. In log-in authentication, however, after authentication is performed at the start of use, whether the user is the person who authenticated is not continuously monitored. Therefore, if the mobile information terminal is used by another person for some reason after log-in authentication, the other person can operate the mobile information terminal without performing log-in authentication. Such a security vulnerability in log-in authentication has been a problem. To solve this problem, Patent Literature 1 discloses a portable information terminal in which the positions where the user using the terminal grips the terminal when performing authentication are acquired by a plurality of pressure sensors and recorded; if, after authentication, the positions where the user grips the terminal are changed by a specified distance or more, the required data input by the user to use a service is invalidated and the validity of the authentication already performed is cancelled. Therefore, even if the terminal is stolen during the act of inputting data required to use a service after authentication, the authentication and the data input by the user are invalidated when the user's hand is separated from the terminal. To use a service after the authentication is invalidated it is necessary to perform authentication again. Therefore, this terminal can effectively prevent unauthorized use by a third party.